code: def _comb(self, N, k):
      val = numpy.float64(1)
      for i in range(k):
          val *= (N - i) / (k - i)
      return val
  
imports: import unittest
  import numpy
  import pytest
  import cupy
  from cupy import testing
  from cupy.testing import _condition
label_desc: Use image node_id 4 for calling the TestPermutationRandomness obj's underlying member method code with example usage: obj._comb(N, k) and returns: val